rxjs fromEvent的用法

import { of, fromEvent, interval, Observable } from 'rxjs';
import { Injectable } from '@angular/core';
import { map, switchMap } from 'rxjs/operators';
import { tap } from 'rxjs/operators';
import { OperatorFunction } from 'rxjs';

@Injectable()
export class JerrySandBoxService{
    name = 'Jerry';
    jerryMap: OperatorFunction<Event, number> = switchMap(this.jerryintervalFunction);

    jerryintervalFunction(event: Event){
        console.log('event: ' + event.timeStamp );
        /*
        returns an Observable that emits an infinite sequence of ascending integers, with a constant interval of time of your choosing between those emissions.*/

        //const a = interval(1000);
        //return a;
        // return event.timeStamp;
        return of(event.timeStamp);
    }
    print(){
        /*
        const observable = of(1, 2, 3);
        const newObservable = observable.pipe(
            tap(num => console.log(num)),
            map(num => 'hello world: ' + num)
        );
        newObservable.subscribe(data => console.log('in subscribe: ' + data));*/
        const clicks: Observable<Event> = fromEvent(document, 'click');

        const result = clicks.pipe(this.jerryMap);
        //result.subscribe(x => console.log(x));
        result.subscribe(x => {
            console.log(x);
        });
    }
}